Phase modulation schemes—techniques that convey information using the phase of the carrier signal—are effective communication methods. A popular phase modulation scheme is quaternary phase shift keying (QPSK).
FIG. 1 shows a constellation diagram that illustrates how QPSK maps two-bit digital data to one of four offsets. FIG. 2 shows a typical QPSK (or I/Q) modulator used to generate a phase-modulated signal. This technique relies on orthogonal signal vectors to realize the phase offsets—an inherently linear technique, since it depends solely on the matching of these orthogonal signals.
However, the typical I/Q modulator requires several power-consuming circuits to generate the orthogonal signals. It would therefore be advantageous to have a low-power highly linear phase modulator that is highly integrated.